1. Field of the Invention
The present invention relates to a combination faucet device, and more particularly to a combination faucet device for mixing hot water with cold water by pressing a movable valve member with a spring composed of a material having a spring constant varied according to the temperature.
2. Description of the Related Art
One example of proposed combination faucet devices is an automatic temperature-control combination faucet disclosed in JAPANESE UTILITY MODEL PUBLICATION GAZETTE No. 61-44062, where a shape-memory alloy whose shape is varied with the temperature is used to press a movable valve member for changing the ratio of hot water to cold water, thus uniformly controlling the temperature of water mixture of hot water and cold water. After a predetermined shape is given to the shape-memory alloy in an atmosphere of a specific temperature, the alloy is physically changed to another shape at other temperatures. The original predetermined shape is, however, restored every time when the alloy is exposed to the atmosphere of the specific temperature. The shape-memory alloy has a thermal capacity smaller than conventional temperature-sensitive elements, for example, a thermowax, and is sensitive to the temperature variation.
In the prior art combination faucet, the movable valve member is pressed on one end thereof by a shape-memory alloy coil and on the other end thereof by a coil spring. The shape-memory alloy coil is directly exposed to water mixture of hot water and cold water. The shape-memory alloy coil having a fixed coil length at a specific temperature functions as described below in response to the temperature variation of water mixture.
While water mixture is in a steady state at a preset temperature, the movable valve member does not move but is stopped at a position where the shape-memory alloy coil balances with the coil spring. When the temperature of water mixture is changed from the steady state to the specific temperature by an external turbulence, the shape-memory alloy coil exerts its shape restoration effect to restore the fixed coil length set at the specific temperature. The shape restoration effect destroys the balance of the shape-memory alloy coil with the coil spring to drive the movable valve member towards the coil spring or the shape-memory alloy coil. When the coil length of the shape-memory alloy coil is successively set in a certain temperature range around the preset temperature, the shape-memory alloy coil exerts its shape restoration effect to vary the coil length with variation in the temperature of water mixture within the certain temperature range. The movable valve member is accordingly displaced corresponding to the temperature change of water mixture so as to vary the ratio of hot water to cold water, thus maintaining the temperature of water mixture around the preset value.
The shape-memory alloy is generally expensive and preferably composed of a small amount of material. A temperature-sensitive spring composed of a small amount of material has a smaller spring constant than conventional springs, and does not drive the movable valve member with a sufficiently large driving force. Such a temperature sensitive spring having a small spring constant has a poor supporting force with respect to the movable valve member. Even a slight torsional force inclines the movable valve member to deteriorate the sealing effects, thus preventing the temperature of water mixture from being controlled accurately.
A spring composed of the shape-memory alloy sensitively responds to the temperature of water mixture of hot water and cold water. When the shape-memory alloy spring is exposed to insufficiently mixed hot water and cold water, varying loads are applied onto different parts of the shape-memory alloy spring to prevent stable temperature control of water mixture.